I also see this since I did a safe-upgrade on sid today and rebooted the machine.
nm is unable to establish the wireless link, unless ipv6 is disabled.
Even unchecking "Require IPv6 addressing for this connection to complete" doesn't help.
Only disabling IPv6 on the link seems to be a workaround to the issue.
Syslog shows this:
Feb 15 12:26:04 milhouse NetworkManager[2134]: <error> [1329305164.622525] [nm-system.c:1061] nm_system_replace_default_ip6_route(): (wlan0): failed to set IPv6 default route: -1
The IPv6 setting was set to "automatic".
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Greetings, Michael.